A major project of this section is the development of new statistical genetics methodology as prompted by the needs of our applied studies. This year Dr. Bailey-Wilson worked on development of several new methods. The first, in collaboration with Dr. Gloria Ho, is an extension of the Transmission Disequilibrium Test (TDT) and the Sibling-Transmission Disequilibrium Test (S-TDT) and the combined test (C-TDT) to traits that are caused, in whole or in part, by loci on the X chromosome. This work was published in the American Journal of Human Genetics in 2000. The second project, in collaboration with Dr. Silvano Presciuttina from the University of Pisa, is the development of a stepwise procedure for using a few genetic markers at each step to try to differentiate siblings from unrelated individuals. This methodology has applications in linkage analysis and in forensics. A new version of this method using likelihood methods has been developed this year and a a manuscript is in preparation. The third project, in collaboration with Dr. Jim Malley at CIT, NIH, is the development of a new method for family based association tests that appears considerably more powerful than the TDT but more robust to false positives than is case-control association. These projects are ongoing.